The Noble-Abel Equation of State: Thermodynamic Derivations for Ballistics Modelling
DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION EDINBURGH (AUSTRALIA) WEAPONS SYSTEMS DIV
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Accurate modeling of gun interior ballistics promotes more efficient gun and propelling charge design. In order to simulate interior ballistic flowfields, such models require a description of the thermodynamic behaviour of the propellant gas. The Noble-Abel equation provides a simple and reasonably accurate equation of state for propellant gases at the high densities and temperatures experienced in guns. Most computational fluid dynamics-based ballistics models, however, require additional thermodynamic functions which must be derived from the equation of state. This note presents the derivation of such thermodynamic functions for Noble-Abel gases. Although the derivations are geared toward the functional requirements of the commercial Fluent code, the results are equally applicable to all computational fluid dynamics solvers. Also presented is a brief numerical example for a typical propellant highlighting the different thermodynamics of the Noble-Abel and ideal gas equations.